Coupling system for multiple wave band circuits



Feb. 21, 1939. l J, Q RE|D ET AL COUPLING SYSTEM FOR- MULTIPLE WAVE BANDCIRCUITS Bmaentor Feb. 21,1939. J. D, REID ET A. I 2,148,039

COUPLING SYSTEM FOR MULTIPLE WAVE BAND CIRCUITS Filed April 27, 1957 2Sheets-Sheet 2 Patented Feb. 21, 1939 UNITED STATES PATENT oFFlcr.Y

CUPLING SYSTEM FOR MULTIPLE WAVE BAND CIRCUITS Delaware ApplicationApril 27, 1937, Serial No. 139,122

6 Claims.

The present invention relates to multiple wave band receivers, and moreparticularly to high frequency interstage coupling systems therefor. Ithas for its primary object to provide an improved interstage couplingsystem for the high frequency amplifier circuits of a multiple wave bandreceiver.

It is a further object of the present invention to provide simplifiedcompound coupling means 10 in a system of the above character, whereintwo primary windings, resonant at different frequencies, are renderedeffective as compound coupling means in conjunction with one or moretuned secondary windings.

It is also a further object of the invention to provide a compoundcoupling system for the higher frequency tuning bands of a multiple waveband receiver, wherein a low distributed capacity provided by oneprimary winding may be utilized to tune a second primary winding,whereby said second primary winding may function in two differing wavebands to provide improved energy transfer at the high frequency end ofeach wave band.

It is also an object of the present invention to provide a highfrequency interstage coupling means for wave band change apparatus andthe like, wherein two `primary windings are included v in series in theoutput circuit of an amplier tube and are coupled to two diiieringsecondary windings, and wherein the series connection pro-f vides a lowdistributed capacity of one primary winding in connection with thesecond primary winding, without requiring the high frequency circuitconnections to be broken therebetween in wave band changing.

It is also a still further object of the present invention to provide aswitching arrangement for the high frequency tuning bands of a multiplewave band receiver, wherein the secondary windings of adjacent tuningbands are operated in parallel in the highest frequency band, therebyminimizing switching connections.

It is also an object of the invention to simplify the switchingarrangement and to provide a more effective energy transfer betweenprimary and secondary circuits for the ultra high frequency tuningranges of a multiple wave band receiver.

A multiple wave band tuning system to which the coupling system of thepresent invention particularly relates is shown, described and claimedin an application of John D. Reid, Serial No. 118,631, for Multiple waveband receivers, filed December 31, 1936. The present application relatesparticularly to the specific circuits and means employed in the C and Dbands for resonating the compound primary windings, and the use of theshunt connected compound secondary windings as referred to in thatapplication.

The invention will, however, be better under- 5 stood from the followingdescription, when considered in connection with the accompanyingdrawings, and its scope will be pointed out in the appended claims.

In the drawings, Figure 1 is a schematic circuit 10 diagram of a radiofrequency amplifier switching system embodying the invention, and

Figures 2 and 3 are similar schematic circuit diagrams showing theconnections provided by the switching system of Fig. 1 in two high frel5quency tuning bands.

Referring to Fig. 1, the circuit includes coils 5, ii, 'I, 8, 9 and IIlforming an inductance unit for tuning Lthrough four differing wave bandsby means of a common variable tuning capacitor 20 section I I, inconnection with the rst detector I2 of a superheterodyne receiver whichis arranged Y to receive amplified high frequency signals from aradiofrequency amplifier tube indicated at I3.

The coil' system provides a band tunable or 25 multiple wave couplingmeans between the radio frequency amplifier tube I3 and the firstdetector I2, and may be considered as the radio frequency tuning meansof the receiver. A separate coil unit comprising a primary winding I4and a sec- 30 ondary winding I5 is provided for the fifth and highestfrequency-tuning range.

The tuning ranges referred to may include such HX, A, HBH, NCH Dcovering a frequency range in each bandas in- 35 dicated below:

l i Kilocycles X band 410 A band 530- 1800 B band 1800- 6500 40 fC bandT A 6500-22000 D band 22000-60000 connections are such that the windingi0 is in- 50A cluded permanently `in theanode circuit I6 of theamplifier I3 adjacent to the anode thereof and is connected in serieswith the highest frequency band` primary winding I4 through a lead I1.The anode circuit, including the series windings, 55

receives anode potential through a lead |8, the highest inductancewinding 5, and a connecting lead I9.

The coils 6 to 9, inclusive, are arranged to form, each in turn, themain secondary windings for the X, A, B and C bands, as indicated by theletters adjacent to the coil sections, and are connected in series, withthe winding 9 connected at its high potential end 20 to the grid circuit2| of the detector |2 and to the stator of the tuning capacitor Couplingwith the grid is provided by a coupling capacitor 22 and a grid resistor23. By this arrangement the tuning capacitor is connected permanently tothe high potential terminal of the coil 9 which is the C band secondary,and to the grid circuit of the detector. without switching connections.

The end terminals of the series connected coils or windings and thejunctions between the coils are connected to a band change switchsection at spaced fixed contacts 25 to 29, inclusive, as indicated.Further spaced fixed contacts are provided on the switch as indicated at30, 3| and 32. A .grounded capacitor 33 is connected with the switchcontact 30 and a series of grounded trimmer capacitors 34, 35, 36 and 3lare connected with the switch contacts 32. The contacts 3| in the switchare not connected in circuit. The low potential terminal 38 of the coil6 and the contact 25 are coupled to the high potential end of the coil 5and the lead I9 through a coupling capacitor 39.

The switch is preferably of the rotary type, and is provided, inaddition to the xed contacts referred to, with three fixed Contactstrips or elongated contact elements 40, 4| and 42, which are located inspaced relation to the fixed contacts to provide the arrangementschematically illustrated, whereby certain bridging connections may bemade between the fixed contacts by three movable contact elements in aseries of steps. The first is a bridging contact 43 which is movablealong the grounded contact 4|, to provide a bridging ground connectionwith the fixed contacts 25 to 28, progressively to the C band positionshown, wherein the low frequency endof the C band coil or secondary 9and the adjacent terminal end of the B band coil 8 are` connected toground. In the next position, for the D band, bridging connection ismade between the contact 40 and the contact 29 to connect the D bandsecondary I5 in parallel with the secondary 9.

'I'he second movable bridging contact element is indicated at -45 and,in the C band position shown, provides a bridging connection between theterminal 29 and one of the terminals 32, for connecting the trimmercapacitor 34 in parallel with the secondary coil 9 to adjust the tuningat the high frequency yend of the C band.

The third movable connection comprises a bridging element v47, for shortcircuiting the coils 6 and 1, whereby they are ineffective to absorbenergy or to resonate in the "C band tuning range, and for bridging theterminals 30 and 42, whereby the capacitor 33 is connected substantiallyin shunt with the coil 8 to provide proper response in the C band as thelow frequency pr"- mary of a compound coupling for the plate circuit I6of the radio frequency amplifier |3 and the C band secondary coil 9, aswill hereinafter be described. The contact 42 is also connected to theanode circuit between the coils |0 and. |4 with the lead through abypass capacitor 48 and a lead 49, whereby the series anode circuitconnection, including the primary I4 for the D band,

is bypassed to place the winding 8 or B band secondary in series withthe winding |0. The latter is in inductive coupling relation to thesecondary 9 and provides a high frequency primary in conjunction withthe winding 8 as the low frequency primary for the C band tuning range.

The switch connections established for the C band tuning are indicatedmore clearly in Fig. 2 in which the same reference characters areapplied to like parts, as in Fig, 1.

Referring to Fig. 2, along with Fig. 1, the C band primary circuitoutlined is also connected with a shunt path through the coil I4, thelead I9 and the capacitor 39. This path has a relatively high impedance,as the X band primary coil 5 is of relatively high inductance and is inseries with the primary coil |4 which also has an appreciable inductanceeffective in the C band range. In the main primary circuit, the bypasscapacitor 48 is of relatively high capacity and low reactance; forexample, it may have a capacity value of .01 microfarad. Therefore, thedesired primary circuit is obtained for the windings |0 and 8 withoutadditional switching contacts to make and break additional circuits.

The plate capacity of the R. F. amplifier tube |3 and other straydistributed anode circuit capacity is indicated at 5|. The trimmercapacitor 33 is connected in shunt with the coil 8 as the low frequencyprimary and is preferably tuned to substantially 4800 kc. for the C bandcovering a range of 6500 to 22,000 kc., as indicated. The low frequencyprimary is therefore resonated below the tuning range of the secondary9.

The distributed capacity 5| is in series with the capacity valueprovided by the capacitor 33, and since the latter is relatively highwith respect to the plate capacity 5|, the plate capacity 5| iseffectively connected in shunt relation to the high frequency primarywinding l0 and serves to tune it, in the present example, tosubstantially 40,000 kcs., which is above the C band tuning range.

The use of a compound coupling of this type is effective to increase thegain through the coupling circuit at both ends of the tuning range,since the high frequency and the low frequency responseof the primarywindings 8 and l0 is effective to raise the overall response of thecoupling system ends of the tuning range.

It has been found that at least one of the primary windings may bemaintained in circuit and utilized in at least two higher frequencytuning bands without switching. It has been found also that that highfrequency primary winding |0 is best adapted for this use, and thereforeis maintained in circuit adjacent to the anode for both the C and Dbands. The D band is higher in frequency, and in order to resonate thehigh frequency primary I0 above the D band, a differing capacity isprovided in series with it and is provided by a suitable low frequencyprimary such as the primary winding 4 which is caused to be effectivefor the D band, in the series anode circuit, by a simple switchingoperation involving only opening the connection through the bypasscapacitor 48 and short circuiting the low frequency primary for the Cband, coil 8 to provide the circuit shown in Fig. 3, to which referencemay be made along with Figs. 1 and 2. Except for the circuit connectionchange for the D band, tuning the circuit is the same as shown in Fig. 3and the same reference numerals are applied.

The low frequency primary coil 4 for the D band is provided with aYrelatively low distributed capacity and is tunable thereby tosubstantially 1900 kcs. or below the D band, and the low distributedcapacity then becomes the controlling capacity in tuning the highfrequency primary I0, since the low distributed capacity of the coil I4is lower than the tube capacity 5 I with which it is effectively inseries. The high frequency primary III operates in both the C and the Dbands, resonating at a frequency above the C band in series with theprimary 8 and its shunt capacity 33, and as shown in Fig, 3 it resonatesat a still higher frequency above the D band when placed in series withthe low distributed capacity of the primary coil I4. In the presentexample the distributed capacity of the coil I 4 is sufficient to tunethe coil I to substantially 90,000 kcs. or well above the D band whichcovers the range of 22,000 t0 60,000 kCS.

In the circuit of Fig. 3, the winding 5 is effective as a choke coil, asin the C band. Howeventhe bypass capacitor 39, while offeringappreciable impedance at 4800 kos., is of relatively low impedance at19,000 kcs and serves as part of the low impedance path to ground fromthe lead I9, as indicated.

By comparing the circuits in Fig. 1 and Fig. 3, it will be seen that thetwo secondary windings I5 and 9 are connected in parallel when theconductor i3 reaches the contacts 29 and 40. The conductor d1 groundsthe contact 28 and also the contacts 25, Z6 and 21.

Since the coil 9 is of relatively high inductance with respect to thecoil I5, parallel operation in the D band has been found to bepermissible and at the same time permits compound coupling wherebyenergy is supplied from the primary winding I0 to the coil 9 and fromthe coil I4 to the coil I5 for the D band operation. By this arrangementthe tuning capacitor I I and the tube input circuit ZI may be maintainedpermanently connected with the major portion of the tuning inductanceunit and likewise necessity for switching the high frequency primary l0is eliminated.

` This winding is closely associated with the winding 0 and remains incircuit throughout the switching operations for the various bands, thuspreventing change in distributed capacity at the sensitive highfrequency end of the tuned circuit.

While the coupling system of the present invention has been shown anddescribed in its application to a radio frequency amplifier stage in theC and D band ranges, it may be provided in other multiple wave bandapparatus between ultra high frequency circuits in a similar manner andin other high frequency and ultra high frequency tuning ranges.

We claim as our invention:

1. In a tunable high frequency multiple wave band amplifier, thecombination of means providing compound inductive interstage couplingbetween certain of the signal conveying circuits thereofand including acoupling winding having low distributed capacity and resonant at afrequency below a predetermined tuning band, a second coupling winding,and means for connecting said windings effectively in series whereby thedistributed capacity of the first winding is effective to tune thesecond coupling winding to a frequency above said tuning band,

2. In a high frequency multiple wave band amplifier, the combination oftwo signal circuits, means providing compound inductive coupling betweensaid circuits including two coupling windings connected in series in onecircuit and resonant at different frequencies, a third coupling windinghaving a low distributed capacity, and means for selectively connectingsaid third winding in series with one of said first-named windings tothe exclusion of the other whereby said distributed capacity iseffective to resonate said one winding to a higher frequency.

3. In a high frequency interstage coupling system for multiple wave bandamplifiers and the like, the combination of two primary windings,resonant at different frequencies above and below a predetermined waveband, a secondary winding tunable through said wave band and coupled toreceive signal energy from said high and low frequency primary windingsjointly, and means for resonating the high frequency primary winding ata frequency above a predetermined higher frequency tuning bandcomprising a second low frequency primary winding, said second lowfrequency primary winding having a low distributed capacity effective toresonate said high frequency primary winding above said higher frequencytuning band.

4. In a high frequency interstage coupling system for multiple wave bandamplifiers and the like, the combination of two primary windings,resonant at different frequencies above and below a predetermined waveband, a secondary winding tunable through said wave band and coupled toreceive signal energy from said `high and low frequency primary windingsjointly, and means for resonating the high frequency primary winding ata frequency above a predetermined higher frequency band comprising asecond low frequency primary winding resonant below said higherfrequency band and connected in series with said high frequency primarywinding, said second low frequency primary winding having a lowdistributed capacity effective to resonate said high frequency primarywinding above said higher frequency band, a higher frequency Secondarywinding tunable through said higher frequency band coupled with saidsecond low frequency primary to receive signal energy therefrom, andswitching means for rendering the rst low frequency primary ineffectiveas a coupling means and for connecting said secondary windings inparallel.

5. In a multiple Wave band receiver, the combination with a radiofrequency amplifier, of an interstage tunable coupling means thereforcomprising an output anode circuit for said amplier, a primary windingpermanently connected in circuit therewith at the high potential end ofthe anode circuit to provide a high frequency primary winding for saidinterstage coupling means, a pair of low frequency primary windings, andmeans for selectively connecting said lastnamed windings serially incircuit with the `firstnamed winding and the anode capacity of saidtube, the distributed capacity of one of said second-named primarywindings being of a value lower than the anode capacity and effective totune the high frequency primary winding to a predetermined highfrequency when connected in circuit therewith.

6. In a multiple wave band receiver, a combination with the radiofrequency amplifier, of an interstage tunable coupling means thereforcomprising an output anode circuit for said amplifier, a primary windingpermanently connected in circuit therewith at the high potential end ofthe anode circuit to provide a high frequency primary winding for saidinterstage coupling means, a pair of low frequency primary windings, andmeans for selectively connecting said lastnamed windings serially incircuit with the vfirstnamed winding and the anode capacity of saidtube, the distributed capacity of one of said second-named primarywindings being of a value lower than said anode capacity and effectiveto tune the high frequency primary winding to a predetermined highfrequency when connected in circuit therewith, a pair of secondarywindings one coupled with each of said low frequency and high frequencyprimary windings, a second tube having a grid circuit, a variable tuningcapacitor, circuit means permanently connecting said capacitor and gridcircuit with one of said secondary windings, and means for connectingsaid secondary windings in parallel conjointly operable with saidfirst-named selecting means.

JOHN D. REID.

LOREN R. KIRKWOOD.

